Rheological behaviour of fresh Portland pastes with siliceous mineral additions: silicafume, diatomite and quartz

PEDRAJAS, C.; RAHHAL, V.; BLÁZQUEZ, A.; RÍO, O.; TALERO, R.

Beijing

Congreso; 14th International Congress on the Chemistry of Cement (ICCC 2015),; 2015

14ICCC

AbstractThe rheological behavior of fresh Portland cement (PC) pastes with different chemical and potential mineralogicalcompositions was analyzed alone and when blended with siliceous mineral additions: silica fume, diatomite and quartz, which had a SiO2 content of over 90%. The replacement ratios used were 20 and 40% for mineral additions quartz anddiatomite, and 5 and 15% for silica fume, all by Portland cement weight. Trials were conducted during latent hydrationat 25 ºC and were designed to find the most significant thixotropical behavior of all fresh cement pastes. The findingsshowed that the shear stress in every fresh paste was observed to rise with C3S (%) content of the PC and hence with adecrease in its Na2Oeq.(%) content, which actually proved to be the key determinant for apparent viscosity of both freshPC pastes. Further, then, to the potential mineralogical composition of the two Portland cements and therefore to thenature and development of the hydration products formed, the PC with higher C3A (%) content, i.e., the one with thehigher Na2Oeq.(%) content, performed best in the rheological study, as logical. The siliceous mineral additions werelikewise observed to affect fresh paste rheology with both types of PC, depending, firstly, on whether or not they werepozzolanic, and secondly, on their morphology and particle size and the type of PC. Thus, they were observed tostimulate Portland cement hydration differently: directly and non-directly or, if they were very pozzolanic, indirectlyabove all. In addition, depending of the mineral addition deemed, dilution also had a direct and inevitable effect on the rheological properties of their fresh pastes.